Our heroes corner Kara in the third act and, long story short, ask if she would kindly put Spock's brain back. As it happens, Kara is no longer up to the task. Her surgical skills have vanished, repossessed after she missed a couple of student loan payments, I guess. She claims to have no neuroscience knowledge whatsoever, which is rather odd for someone who only hours ago had a suspicious tub of formaldehyde rolling around in the trunk of her car like Thomas Harvey. Brain and brain, what is brain? Kara famously ruminates when pressed, truly a question for the ages.
There's an explanation for all this involving a magic thinking helmet, and much else besides, none of which need concern us presently. As usual, a plot ex machina arrives and all ends well. Kara gets her comeuppance and Spock gets reunited with his puzzler, sans PTSD or any long-term consequences at all really. I reckon everyone had a good laugh about it down at the space VFW. Hey, Spock. Remember the time some crazy woman SCOOPED OUT YOUR BRAIN? That sure was a hoot!
However, you must admit Kara has a point. What is brain?
We can arguably date the founding of brain science to the Greek physician Galen, who established thinky stuff goes on in the head and not in the heart, as had been previously believed. This by noting where gladiators got maimed and their concomitant deficits. We have amassed a mountain of brain facts in the two millennia interim, on everything from its molecules to its operation. And yet, a concise definition of just what the heck the thing is remains elusive.
The Palace of Memory, the brain has been called. Think box. Gray matter. Smarts. The anatomists study gyri and sulci, the arrow anatomists projections and nuclei. To computationalists, the brain is valves or op amps or logic gates or whatever real-life computational device is in vogue. The computer scientists see tree searches and pattern matching and predicate logic. The engineers see frequencies and filters and feedback. The physicists see a collection of sources and sinks, or an assembly of coupled oscillators, or a gaggle of renewal processes. To the philosophers the brain is the seat of the soul. To the romantics, a mystery. The psychologists just call it trouble.
The brain is all of these things and none of them. It is like the parable of a group of blind men squeezing on an elephant. Each identifies something different. How can we understand a thing if we cannot even decide what it is?
As with most things in life, it falls to LabKitty to light the way forward. Stand back as I unsheathe the gleaming Sword of Truth.
The brain is a cheap plastic correlation receiver.
As this has been an open question for some 2000 years, I suppose I'm obligated to expand upon my bold denouement. Very well. There are three parts to the definition: (1) cheap, (2) plastic, and (3) correlation receiver. Let us take each in turn, beginning with the last.
3. Correlation Receiver
A filter is familiar to anyone who has listened to music. A low-pass filter admits low-frequency signals and rejects high-frequency signals. This is called bass. A high-pass filter admits high frequencies and rejects low. This is called treble. More sophisticated audio gear comes equipped with an equalizer, a collection of bandpass filters each friendly to a window of frequencies and blocking all others.
Low-, high-, and band-pass are not the end-all of filter design. We may devise a filter that prefers a specific kind of signal. In effect, we tell the filter what to listen for. The filter reports how closely its current input matches its given reference template, and so is called a matched filter. The matching process is implemented by correlating the received signal with the template, so a matched filter is also known as a correlation receiver. When the template signal is present, the receiver responds vigorously. When it is absent, it does not respond at all. In between are shades of grey -- inputs offering a degree of match, a probability of a response.
The brain is a correlation receiver made flesh. Each neuron is hardwired to a collection of inputs, defining a pattern the neuron accepts while forsaking all others. Anatomy is destiny. Yet, a neuron may receive hundreds or thousands of inputs, none of which sufficiently powerful in isolation to coax the neuron to respond. The inputs must overlap. This defines a spatio-temporal reference template, cooperative in space and coordinated in time.
And hierarchical in organization. Not only do the senses impinge upon the brain, so does the brain itself. The neurons that recognize Beethoven are not the ones that recognize Mondrian. But the ones that recognize Mondrian are not the ones that recognize shapes. Or lines. Or color. A biological Ponzi scheme is at work, each actor waiting for the proper signals to act and broadcasting its findings to whomever is listening. Eventually, the motoneurons are listening. Their output is behavior and the processing is complete. Stimulus and response, the alpha and omega of the human condition.
A demonstration. Raise your hand when you hear your name.
Aardvark. Capybara. Sailfish. < insert your name here >.
The spectral content of each word activates a collective of hair cells in the cochlea, each with a template comprising a narrow band of audio frequencies. Their output travels via the eighth cranial nerve to the cochlear nucleus, to neurons of the superior olivary complex, to the nuclei of the lateral lemnisci, then to the inferior colliculus and medial geniculate, and finally arrive at the superior temporal gyrus of auditory cortex. At each station, the reference template becomes more sophisticated, more abstract -- frequencies to formants, formants to syllables, syllables to words -- until at last your name is heard. A new template created only moments ago by instructions from an Internet stranger signals motoneurons in your pre-central gyrus.
And, now, here you sit with your hand in the air. Anatomy is destiny.
Or not. You may have missed your calling. The list ended plumb, bob but you heard plumb bob. Conversely, you may have risen in error. Play-doh was called, but you heard Plato. The correlation receiver doesn't care. It makes mistakes. It says it is when it ain't; it says it don't when it do. To a hammer all things look like a nail. To a correlation receiver, all things look like its reference template. The only nuance is how much?
Anatomy is destiny.
2. Plastic
The correlation receiver springs from womb equipped with a competent set of reference templates. Fish gotta swim, birds gotta fly, LabKitty gotta eat those fish and birds, and none required training to do so. Beavers construct dams and ants excavate elaborate underground cities without ever setting foot in engineering school. Richard Dawkins calls this the extended phenotype. Robert Pinsky called it "serpent knowledge."
These built-in behaviors can be quite impressive. However, the true wonder of the correlation receiver is that it can be altered. Improved. Expanded. The newborn foal rises to shaky legs but soon gallops. The puppy learns to fetch, the lab rat learns to press a bar. Merlin may have greeted his mother's midwife in Latin, but you and I did not. And yet, this fine morning we say Salve! Something has changed.
That change is properly called neuroplasticity. We might call it "learning," but doing so risks misunderstanding. The label conjures an image of the classroom, of lesson, of drill and memorization. That is plasticity, but plasticity is more. In every waking moment, and other moments too, the brain continuously adjusts itself. Pink Floyd don't need no education, but they get it nonetheless.
The substrate of plasticity is an alteration of the connections between neurons -- the synapses. This comprises both a tweaking of the extant synapses and the creation of new ones. The details will not concern us, save to say it happens always. Learning is not something you do, it is something you are. Every event alters synapses. Slowly. Imperceptibly. Usually. Information arrives at the brain and leaves it changed. We are both processor and the processed.
When you look into an abyss, the abyss also looks into you -- Nietzsche the neuroscientist. Just reading this sentence changed your brain in some small way: LabKitty causes brain damage! But so does everything else. Your fancy liberal arts education that buried you under $100K in student loan debt? If we could crack open your skull and do equivalent synaptic rearrangement under the knife, you couldn't tell the difference.
It is plastic, your correlation receiver.
1. Cheap
Every living thing comes equipped with its own plastic correlation receiver. Except for plants. And bacteria. And protozoa and diatoms. Yeast. Jellyfish perhaps. And a few of my in-laws.
Still, most everything that walks or flies or swims has one. Humans alone provide billions and billions of the things. Making another one is easy. All you have to do is get my sister drunk. And, as simple economics tells us, the more of something there is, the less that something is worth. Let's see if we can hang a number on that.
The human brain contains about a hundred billion neurons. It weighs about three pounds. Brain sells for $0.99/pound down at the rendering plant. That works out to about $negligible per neuron.
The classic 741 op amp contains about two dozen transistors. It costs about half a buck (plus S&H). That's more than a penny per transistor. A fortune in Neuros. And all a 741 can do is calculus.
Neurons are cheap in the extreme. They are also cheap in the other sense of the word: Shoddy. Chintzy. Poorly constructed. The performance of an ENIAC vacuum tube puts the average neuron to shame. Neurons can't hold a voltage for any appreciable amount of time. They're contaminated by substantial shot noise. They're grossly nonlinear at low and high frequencies. They're variable in response. Sometimes they don't respond at all. Neurons are sensitive to changes in temperature and pH and osmolarity (the brain's blood supply requires extra filtering, which is why medicines like antibiotics can't get in). And they're slow. If fiber optics had the propagation speed of a typical axon, we'd have built the Internet using semaphore flags.
Neurons also die, and not just every now and then. They get culled in vast numbers over the course of normal adulthood. Unless you are an adolescent, you had substantially more brain cells when you began reading this article than you do now, and that is not my fault. Biologically speaking, about the only nice thing we can say about neurons is they don't turn cancerous (forever stuck in G0, they are). Alas, we have glia for that.<
Still, neurons are a right bargain all things considered. How strange that the most sophisticated computational instrument known is also the cheapest. Think about it: The device responsible for Dies Irae, Hamlet, and quantum mechanics is edible. You can eat it. You can eat it! On the one hand, it put a dune buggy on Mars and sussed the genetic code. On the other, it makes for a nice Gulai Otak.
Your cheap plastic correlation receiver.
Epilogue
One can't help but wonder: If the Eymorg could acquire neurosurgery and starship infiltration skills using their magic thinking helmet, why did they need Spock's brain in the first place? I'm sure somewhere a steadfast defender of the episode has an ironclad explanation. If you can find one.
Cast and fans alike loathe Spock's Brain. It was the beginning of the end. The 3rd and final season of TOS also gave us space cowboys and indians, space Greeks and space hippies, simulated Abe Lincoln and hydrocephalic torture porn and aliens made from pure plucky energy. It wrapped with Captain Kirk in lipstick and, finally, cancellation. Perhaps it was for the best. (Although let's not pretend there weren't just as many misfires when your grandiloquent Captain Picard took command. The first season of TNG is nigh unwatchable, even for die hard fans. Jewels like The Best of Both Worlds and Yesterday's Enterprise were years away and even then -- and in every ST permutation that followed -- you never could predict if the writers were going to lose their marbles in any given week.)
The most poignant tribute to Spock's Brain may well be its unexpected contribution to neuroscience. Whatever its faults, the episode led us to here. On some back lot at Paramount, in the year Apollo 8 circumnavigated the moon and the Tet offensive raged in Vietnam, Gene L. Coon working under a pseudonym penned the question that almost a half century later would help put to rest an enigma vexing the sages since Plato founded his Academy. Brain and brain, what is brain?
We have answered Kara at last.
Image credit: Gaetan Lee via Wikipedia.
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